This invention relates to indicia-marked electrical cable.
As shown in FIG. 1, an armored electrical cable 10 used, for example, to wire buildings has insulated wires 12 encased in a helically wound steel sheath 14. To install the cable, the wires at each end of the sheath are stripped of insulation 16, and the exposed conductors 18 are connected to terminals or other wires inside of a junction box, switch box or other enclosure.
The installer knows which connections to make at each end of the cable because the wire insulations are color-coded. For example, a ground wire may have one color, and wires carrying different phases of AC power could have other colors. The insulation colors are often dictated by industry practice. A cable used for a particular purpose, such as to wire three-phase 277-volt power, typically has several (e.g., four) internal wires and a particular combination of color-coded insulations on the wires. The insulation colors may comply, for example, with the B-O-Y (brown, orange, yellow) convention, in which brown, brown and orange, or brown, orange and yellow, are used depending on the number of internal wires that need to be marked in the cable. In addition, common and ground wires in the cable may have gray and green insulations. The installer (or someone who maintains the cable after installation) can easily identify the purpose of a given cable (e.g., that it is a 277-volt cable) by the predefined combination of insulation colors that are associated with that purpose.
As shown in FIG. 2, once the installation is done, the sheath 14 and the junction boxes 20 at both ends of the cable hide the internal wires from view.
The sheath of a cable can be marked to indicate the function of the cable as described in U.S. Pat. No. 5,350,885, incorporated by reference. The markings can include color-coded coatings and patterns.
In general, in one aspect the invention features an electrical cable including a sheath that envelops at least two internal conductors, and an indicia visible on the sheath and representative of the internal conductor.
One of the advantages of the invention is that someone who is familiar with the combination of indicia used on the conductors to imply a particular function for the cable can identify the function by looking only at the sheath.
Implementations of the invention may include one or more of the following features. Conductor indicia may be visible on the internal conductors. There may be at least two different conductor indicia that are visible on the internal conductors, and at least two different sheath indicia that are visible on the sheath, the sheath indicia being representative of the combination of internal conductors. The sheath indicia may be indicative of the conductor indicia on the conductors. The internal conductors may include electrical wires. The conductor indicia may include the colors of insulation on the conductors. The conductor indicia may be visible at multiple locations along the length of the conductors. The indicia may be visible at multiple locations along the length of the sheath. The sheath indicia may be the same as least one of the conductor indicia. The sheath may include a helically wound metal strip bearing the sheath indicia. The sheath indicia may include a stripe of ink around the circumference of the sheath. The indicia may be representative of a function of the cable. There may be electrical connections between ends of the conductors and terminals or other conductors, junction boxes may contain the electrical connections, and the conductor indicia may be hidden by the sheath and the junction boxes.
In general, in another aspect, the invention features a method of forming a cable by applying a sheath indicia along the length of a surface of a strip of material, wrapping the strip of material to form the sheath, and using the sheath to envelop internal conductors on which conductor indicia are visible, the sheath indicia being representative of the internal conductors.
In general, in another aspect, the invention features an electrical cable including a sheath that envelops an internal conductor, and an indicia visible on the sheath and symbolizing a gauge of the internal conductor.
Other advantages and features will become apparent from the following description and from the claims.